DE10297484T5 - Method and device for producing a granulated rare earth alloy powder and method for producing a rare earth alloy sintered body - Google Patents

Abstract

A process for producing a granular rare earth alloy powder, the process comprising the steps of:
Production of a rare earth alloy powder;
Generation of residual magnetization in the powder; and
Granulating the powder using the agglomeration force generated by the remanent magnetization of the powder.

Description

technical area

The The present invention relates to a method and an apparatus for the production of a granulated rare earth alloy powder and a method of manufacturing a rare earth alloy sintered body.

State of technology

On Rare earth alloy sintered magnet (permanent magnet) is usually made by pressing powder of a rare earth alloy, sintering of the resulting powder compact and then carrying out a Aging treatment with the sintered body. Permanent magnets that currently in large Scope for Various uses are used, including magnets Rare earth metal cobalt base and rare earth metal iron boron base magnets. Among other things, the magnets are based on rare earth-iron-boron (hereinafter referred to as "magnets referred to as "R-Fe-B-based", wherein R for one of rare earth elements including Y, Fe for iron and B for Boron) are becoming increasingly common used in various electronic devices. This is on it attributed to that a R-Fe-B-based magnet has a maximum energy product that is higher than any of the various other magnet types and that it is nevertheless relatively cheap is.

An R-Fe-B-based sintered magnet comprises a main phase, which essentially consists of a tetragonal R ₂ Fe ₁₄ B compound, an R-rich phase, which contains, for example, Nd, and a B-rich phase. In the R-Fe-B-based sintered magnet, part of the Fe may be replaced by a transition metal such as Co or Ni, and part of the boron (B) may be replaced by carbon (C). An R-Fe-B based sintered magnet to which the present invention is advantageously applicable is disclosed, for example, in U.S. Patent No. 4,770,723 and 4,792,368 described.

at In the prior art, an alloy based on R-Fe-B is produced as a material for such a magnet by using a block casting process. In a block casting process usually become a rare earth metal, electrolytic Iron and a Ferrobuor alloy as the respective starting materials by using an induction heating process for melting brought and then the melt thus obtained is in a mold relatively slow cooled, causing an alloy block is obtained.

Recently, a rapid cooling process such as a belt casting process or a centrifugal casting process has received much attention in the prior art. In a rapid cooling process, a molten alloy is brought into contact with and cooled relatively quickly by means of a single quenching roller, a double quenching roller, a rotating disc, or the inner surface of a rotating cylindrical mold, thereby producing a solidified (solidified) alloy from the molten alloy which is thinner than an alloy block. The solidified alloy thus produced is hereinafter referred to as "alloy flake" or "alloy lamella". The alloy flake made using such a rapid cooling process typically has a thickness of about 0.03 mm to about 10 mm. Using the rapid cooling process, the molten alloy begins to solidify (solidify) from its surface which comes into contact with the surface of the quenching roller. This surface of the molten alloy is referred to herein as the "roller contact surface". In the rapid cooling process, therefore, columnar crystals grow in the thickness direction from the roller contact surface. As a result, the rapidly solidified alloy made using a tape casting process or any other rapid cooling process has a structure that includes a crystalline R ₂ Fe ₁₄ B phase and an R-rich phase. The crystalline R ₂ Fe ₁₄ B phase generally has a minor axis size of approximately 0.1 μm to approximately 100 μm and a major axis size of approximately 5 μm to approximately 500 μm. On the other hand, the R-rich phase, which is a non-magnetic phase, which contains a rare earth element R in a relatively high concentration and has a thickness (corresponding to the width of the grain boundary) of about 10 μm or less is in dispersed the grain boundary between the crystalline R ₂ Fe ₁₄ B phases.

Compared to an alloy produced by the conventional block casting or molding process (such an alloy is referred to here as an "ingot alloy"), a rapidly solidified alloy is quenched in a shorter time (ie with a cooling rate of 10 ² ° C./s up to 10 ⁴ ° C / s). The rapidly solidified alloy therefore has a finer structure and a smaller crystal grain size. In addition, the grain boundary in the rapidly solidified alloy has a larger area and the R-rich phase is broadly and thinly dispersed (distributed) within the grain boundary. The rapidly solidified alloy also has excellent dispersibility of the R-rich phase. Since the rapidly solidified alloy has the advantageous features described above, a magnet with excellent magnetic properties can be produced from the rapidly solidified alloy.

On alternative alloy manufacturing process, the so-called "Ca reduction process (or reduction / diffusion method) "is also from the prior art known. This procedure includes the following treatment and Production stages: addition of metallic calcium (Ca) and calcium chloride (CaCl) either to the mixture of at least one rare earth oxide, Iron powder, pure boron powder and at least one ferrobor powder and boron oxide in a predetermined ratio or in a mixture, which contains an alloy powder or a mixed oxide or a mixed oxide these structural elements in a predetermined ratio; Performing one Reduction / diffusion treatment with the resulting mixture within an inert atmosphere; Dilute the reactant obtained to prepare a slurry and then Treat the slurry with water. In this way, a solid can be made from an alloy can be obtained on an R-Fe-B basis.

It it should be noted that each small block consists of a fixed Alloy is referred to here as an "alloy block". The "alloy block" can be any of different forms of solid alloys that are not only solidified alloys by cooling a melt of an alloy material have been obtained (for example an alloy block which produced by the conventional ingot casting process or an alloy flake made by a rapid cooling process, such as B. a strip casting process has been produced), but also a solid alloy that produced by the Ca reduction process.

On Alloy powder to be pressed is obtained by execution of the following treatment stages: rough pulverization of an alloy block in one of these forms by using, for example, a hydrogen entrapment process and / or any of the various mechanical grinding methods (such as using a disk mill); and fine pulverization of the resulting coarse powder (with an average particle size of 10 μm to 500 μm) Using a dry milling process using, for example a jet mill.

The R-Fe-B-based alloy to be pressed preferably has an average particle size of 1.5 μm to about 6 µm, um to achieve sufficient mechanical properties. It was on it noted that the "middle Particle size "of a powder here, unless otherwise specified is an FSSS particle size. However, if a powder with such a low average particle size is used, are the resulting fluidity, Pressability (including the void fill density and compressibility) and productivity poor.

In order to overcome these problems, a method for coating the surface of alloy powder particles with a lubricant has been proposed. For example, Japanese Patent Laid-Open Publication No. 08-111 308 and in U.S. Patent No. 5 666 635 describes a method for producing a fine alloy powder based on R-Fe-B (with an average particle size of 1.5 μm to 5 μm) by adding 0.02% by mass to 5.0% by mass of a lubricant (e.g. at least a liquefied fatty acid ester) to a coarse alloy powder based on R-Fe-B with an average particle size of 10 μm to 500 μm and then pulverizing the mixture by means of a jet mill within an inert gas.

The lubricant not only improves the fluidity and compressibility (or compressibility) of the powder, but also acts as a binder to increase the hardness (or strength) of the compact. Nevertheless, the lubricant can also remain as residual carbon in the sintered body, where it may impair the magnetic properties. Therefore, the lubricant must have good binder removability. For example, Japanese Patent Laid-Open Publication No. 2000-306753 described as preferred lubricants with good binder removability depolymerized polymers, mixtures of a depolymerized polymer and a hydrocarbon solvent and mixtures of a depolymerized polymer, a mineral oil with low viscosity and a hydrocarbon solvent.

In this method, in which a lubricant is used, a certain degree of ver achieved improvement, but it is still difficult to fill the cavity with the powder sufficiently evenly or to achieve a sufficient degree of pressability. Among other things, a powder made using a belt casting process or any other rapid cooling process (with a cooling rate of 10 ² ° C / s to 10 ⁴ ° C / s) has a smaller average particle size and a narrower particle size distribution than one Powder that has been produced by a block casting process and therefore has in particular poor fluidity. For this reason, the amount of powder to be filled in the cavity may sometimes exceed the allowable range, or the cavity filling density may be uneven. As a result, the variations in the mass or dimensions of the compacts may exceed their allowable ranges, or cracks or chips may occur in the compacts.

As another (further) method to improve fluidity and of an R-Fe-B-based alloy powder proposed to produce a granulated powder.

For example, Japanese Patent Laid-Open Publication No. 63-237 402 described that the pressability can be improved with a granulated powder which was prepared by adding 0.4 mass percent to 4.0 mass percent of a mixture of a paraffin compound (which is liquid at room temperature) and an aliphatic carboxylate to the powder and by grinding and granulating them. A method using polyvinyl alcohol (PVA) as a granulating agent is also known. It should be noted that both the granulating agent and a lubricant act as binders to increase the strength of the compact.

However, when the Japanese Patent Laid-Open Publication No. 63-237 402 described granulating agent is used, the binder removability is so poor that the magnetic properties of a sintered body made of an R-Fe-B-based alloy are impaired (deteriorated) by the carbon remaining in the sintered body.

on the other hand exhibits the granulated powder by using a spray drying process has been made on PVA, a high binding force on it is not too hard to be complete to be able to be crushed even when putting on an external magnetic Field. Therefore can its primary Particles do not respond to the magnetic field sufficiently can be aligned and it can no magnets with excellent magnetic properties were obtained become. PVA also has poor binder removability on and the carbon originating from PVA tends to be in the magnet to stay. However, this problem can be overcome by performing a Binder removal process in a hydrogen atmosphere. It is however, it is still difficult to remove this carbon sufficiently.

In order to solve the problem that the granulated powder is difficult to grind even under an aligning magnetic field, the applicant of the present invention has proposed a method for producing a granulated powder in which the respective powder particles (ie the respective primary particles) which are associated with magnetic powder have been bonded (coupled) with a granulating agent by granulating the powder material in a static magnetic field applied thereto (see Japanese Patent Laid-Open Publication No. 10-140202 ). When this granulated powder is used, the magnetic properties are improved compared to using a granulated powder in which the primary particles which have not been aligned with an applied magnetic field are bound (coupled) with a granulating agent. However, it is difficult to sufficiently align the pressed powder particles with the magnetic field. As a result, the resulting magnetic properties are inferior to a situation where a non-granulated rare earth alloy powder is used.

It various granulating agents and granulation processes proposed as described above. A process for mass production a granulated powder of a rare earth alloy, which has excellent fluidity and has excellent pressability and that for manufacturing of magnets with good magnetic properties can contribute has not yet been developed.

On the other hand, the demand for smaller, thinner and more powerful magnets is increasing. Therefore, the development of a method for manufacturing small or thin high-performance magnets with high productivity is desired. In general, when a rare earth alloy sintered body (or a magnet obtained by magnetizing the sintered body) is machined, its magnetic properties deteriorate as a result of stresses caused by machining. Such a deterioration in the magnetic properties is not negligible for a small magnet. Therefore, the smaller the size of the magnet to be manufactured, the more necessary it is to produce a sintered body which has a high dimensional accuracy in order to avoid any machining at all and which also has the final shape to be produced. For these reasons, too, the demand for a rare earth alloy powder with excellent fluidity and excellent pressability (for example for an alloy powder based on R-Fe-B) is increasing.

description the invention

Around Overcoming the problems described above is a primary object the present invention therein, a method of manufacture of a granular rare earth alloy powder that have good fluidity and has good pressability and the production of a magnet with excellent magnetic properties, as well as a process for producing a high quality sintered body from a rare earth alloy with high productivity.

On Process for producing a granulated rare earth alloy powder according to the present Invention comprises the following stages: manufacture of a rare earth alloy powder; Generation of residual magnetization in the powder; and granulating of the powder by exploiting an agglomeration force caused by the remanent magnetization of the powder is generated to thereby to obtain the subject described above.

The The granulation stage preferably comprises the stage of feeding one kinetic energy to the particles of the powder and the particles preferably grow under the influence of a tumbling effect, which is generated by the kinetic energy, under a magnetic Essentially zero field.

The Process can include the following stages: Preparation of the powder with a remanent magnetization in a container; and delivery of a kinetic Energy to the powder particles under a magnetic field of essentially zero in the container. Alternatively, the process can include the following steps: Manufacturing the powder in a container; Generation of a remanent magnetization in the powder in the container Applying a magnetic field to the powder; and feeding of kinetic energy to the powder particles with the remanent magnetization under a substantially zero magnetic field in the container.

The The method may further include a step of adding a granulating agent to include the powder. Alternatively, the method can also be a Include the step of not adding a granulating agent to the powder.

The Stage of generation of residual magnetization in the powder preferably comprises the step of applying a demagnetizing Alternating field.

This Rare earth metal alloy is preferably an alloy based on R-Fe-B, which is 2 mass percent or more Dy, 1 mass percent or more Tb or 1 mass percent or contains more Dy and Tb.

The Powder preferably has an average particle size of 1.5 μm to 6 μm.

The The granulating stage preferably comprises a stage for producing a granulated powder with an average particle size of 0.05 mm to 3.0 mm.

On A method of manufacturing a rare earth alloy sintered body according to the present invention Invention comprises the following stages: Preparation of a granular Rare earth alloy powder according to one of the above Method; To fill a cavity with a rare earth alloy powder, which comprises the granulated powder without applying a demagnetizing magnetic Field to the granulated powder; Production of a compact by Pressing the rare earth alloy powder, which comprises the granulated powder under an applied thereon aligning magnetic field; and sintering the compact to thereby obtaining the object described above.

On granulated according to the invention Rare earth metal alloy powder is characterized in that it is a rare earth alloy powder with a remanent magnetization and has an average particle size of 1.5 μm to 6 μm, an average particle size of 0.05 mm to 3.0 mm and by means of an agglomeration force which by the remanent magnetization has been generated, is bound (coupled).

• (a) Herstellung eines Seltenerdmetall-Legierungspulvers mit einer remanenten Magnetisierung in einem Behälter durch Anordnen des Pulvers auf einer Basisplatte, die für Luft durchlässig ist;
• (b) Erzeugung eines ersten Gasstromes in dem Behälter, sodass der erste Gasstrom, ausgehend von unterhalb der Basisplatte, nach oben strömt;
• (c) Zuführung einer kinetischen Energie zu den Pulverteilchen mittels des ersten Gasstroms, um dadurch das Pulver zu granulieren unter einem magnetischen Feld, das im Wesentlichen Null beträgt, durch Ausnutzung einer Agglomerationskraft, die durch die remanente Magnetisierung des Pulvers erzeugt worden ist und eines Tumbling-Effekts, der durch die kinetische Energie erzeugt worden ist;
• (d) Erzeugung eines zweiten Gasstromes in dem Behälter, sodass der zweite Gasstrom, ausgehend von oberhalb der Basisplatte, nach unten strömt; und
• (e) Bildung einer Pulverschicht aus dem Pulver auf der Basisplatte und Komprimieren der Pulverschicht mit dem zweiten Gasstrom.

A method for producing a granular rare earth alloy powder according to a preferred embodiment of the present invention is characterized in that it comprises the following steps:

• (a) producing a rare earth alloy powder with a remanent magnetization in a container by placing the powder on a base plate which is permeable to air;
• (b) generating a first gas stream in the container such that the first gas stream flows upward from below the base plate;
• (c) supplying kinetic energy to the powder particles by means of the first gas stream, to thereby granulate the powder under a substantially zero magnetic field by utilizing an agglomeration force generated by the remanent magnetization of the powder and tumbling -Effect created by kinetic energy;
• (d) generating a second gas stream in the container so that the second gas stream flows downward from above the base plate; and
• (e) Forming a powder layer from the powder on the base plate and compressing the powder layer with the second gas stream.

The Procedure is also characterized in that at least part of stage (d) and at least part of stage (b) are carried out simultaneously, to thereby produce the article described above.

at a preferred embodiment includes the period within which stages (d) and (b) are simultaneous carried out are a period of time within which the flow rate of the first gas stream is reduced will while that of the second gas stream is increased.

The Step (a) may include the steps of introducing a rare earth alloy powder without retentive magnetization in the container and the generation of one remanent magnetization in the powder that has no remanent magnetization has and in the container filled has been applied by applying a magnetic field the powder. Alternatively, stage (a) can be the stages of manufacture of a rare earth alloy powder with a remanent magnetization and filling of the powder with the remanent magnetization in the container.

at a preferred embodiment steps (b), (c), (d) and (e) are repeated in this order performed several times.

at another preferred embodiment the method may further comprise a step (f) in which the first Gas flow being stopped while the second gas stream is generated and then the second gas stream is stopped will while the first gas stream is generated again at a flow rate, which is the average flow rate of the first gas stream in step (c), whereby the powder layer, which has been applied to the base plate is crushed. Step (f) can be carried out at least once after step (e), while steps (b) to (e) are carried out repeatedly.

at another preferred embodiment is the rare earth metal alloy based on R-Fe-B.

at a further preferred embodiment the powder has an average particle size of 1.5 μm to 6 μm.

at yet another preferred embodiment is according to the method a granulated powder with an average particle size of 0.05 mm to 3.0 mm.

A method for producing a rare earth alloy sintered body according to the present invention is characterized in that it comprises the following steps: producing a granulated rare earth alloy powder according to one of the methods described above; Filling a hollow space with a rare earth alloy powder comprising the granulated powder without applying a demagnetizing magnetic field to the granulated powder; Producing a compact by pressing the rare earth alloy powder comprising the granulated powder with an aligning magnetic field applied thereto; and sintering the compact.

A Device for producing a granulated rare earth alloy powder according to the invention is characterized in that it comprises: a container which a base plate for includes the inclusion of a rare earth alloy powder; a first Channel that with the container is connected to the production of a first gas stream, the flows from below the base plate upwards in the container; and a second channel that communicates with the container Generation of a second gas stream from above the base plate flows down, in the container.

The Device is as well characterized in that the first and second channels are independent of each other with the container are related, thereby accomplishing the goal described above is achieved.

The The device preferably further comprises a temperature control device and a blower within the first channel.

The The device may also include a buffer tank within the second channel include.

The The device preferably further comprises a control circuit, which is a thermometer for measuring the temperature of the gas in the container includes and the operation of the blower stops at least when the measured temperature reaches a predetermined one Temperature exceeds.

Within of the container positive pressure is preferably maintained while the Device is in operation.

The The device can also include a device for generating a magnetic Include field that is applied to the powder that is on the base plate is arranged.

Short description of the drawings

1 (a) explains in schematic form the structure of a granulated powder according to a preferred embodiment of the present invention and 1 (1b) and 1 (c) explain in schematic form the structure of conventional granulated powders for comparison purposes.

2 explains in schematic form a granulating device 20 for the production of a granular powder from an alloy based on R-Fe-B according to a preferred embodiment of the present invention.

3 explains in schematic form a granulating device 100 for producing a granular powder from an R-Fe-B-based alloy according to another preferred embodiment of the present invention.

4 (a) and 4 (b) are diagrams showing in schematic form how the (flow rates of) gas streams (s) in a container (depending on time) change in a process for producing a granulated powder according to a preferred embodiment of the present invention.

5 Fig. 3 is a graph showing the remanence B _r of sintered magnets made from granulated powders according to specific examples of the present invention and granulated powders according to comparative examples.

Best kind the implementation the invention

A method for producing a granular powder and a method for producing a rare earth alloy sintered body according to preferred embodiments of the present invention will be described below with reference to the accompanying drawings. The features of the present invention are described in the following description of preferred embodiments in their application to a process for producing a sintered magnet from a powder of an R-Fe-B-based alloy which has been produced using a strip casting process and which has excellent magnetic properties but low flowability. However, the present invention is by no means limited to these specific preferred embodiments. Instead, a rare earth alloy powder made by another method can be used instead.

On Method for producing a sintered body from an alloy R-Fe-B base according to a preferred one embodiment The present invention comprises the following stages: Manufacturing an alloy powder based on R-Fe-B (hereinafter referred to as "powder material" or "primary particle powder"); generation residual magnetization in the powder material; Granulate of the powder by exploiting an agglomeration force caused by the remanent magnetization of the powder material has been generated is; Production of a compact by pressing the alloy powder based on R-Fe-B, which comprises the granulated powder with an applied thereon magnetic field; and sintering the compact. By magnetizing of the resulting sintered body using a known method, a sintered magnet can be obtained on an R-Fe-B basis. It should be noted that the magnetization treatment level at any time can be carried out after the sintering process. For example the user of the sintered magnet has the magnetization treatment step perform immediately before using the sintered magnet. also a non-magnetized magnet is referred to here as a "sintered magnet".

In a method for producing a sintered body from an alloy R-Fe-B base according to one preferred embodiment In the present invention, the powder is granulated by using the Agglomeration force caused by the remanent magnetization of the Powder material has been generated. It is therefore possible to either the amount of granulating agent to be added decrease or a binder with a lower binding power to use as a conventional binder. Besides, can even the addition of the granulating agent itself can be omitted.

The features of a method for producing a granulated powder and a resulting granulated powder according to a preferred embodiment of the invention are described below with reference to FIG 1 (a) . 1 (b) and 1 (c) described in more detail. On the left side of the 1 the structures of the respective granulated powders are explained in schematic form. On the right side of the 1 the states of the respective granulated powders to which an aligning magnetic field in a cavity has been applied for the purpose of compaction are schematically explained. The 1 (a) explains in particular a granulated powder 12a according to a preferred embodiment of the present invention, the 1 (b) explains a conventional granulated powder 12b for which a granulating agent has been used and 1 (c) explains a granulated powder 12c , which is described in Japanese Patent Laid-Open Publication No. 10-140 202 described method has been prepared.

As in 1 (a) are shown in the granulated powder 12a of this preferred embodiment primary particles 10a with a remanent magnetization weakly bound to one another (coupled to one another) via a magnetic agglomeration force. In the illustrated example, it is believed that no granulating agent need be used. These primary particles 10a with a remanent magnetization are magnetically coupled together to form a magnetic closed circuit and the remanent magnetization of the granulated powder 12a is very low (for example, it is more than about 0 mT and it is ≤ about 10 mT (Millitesla)). In this granular powder 12a is the remanent magnetization of the primary particles 10a aligned in statistical distribution in contrast to the granulated powder 12c , as in 1 (c) shown. The primary particles 10a can have an average particle size of about 1.5 μm to about 6.0 μm and the granulated powder 12a can have, for example, an average particle size of about 0.05 mm to about 3.0 mm. The residual magnetization can be measured by inserting a probe of a Gauss meter into the granulated powder.

This granular powder 12a has an average particle size and can have excellent fluidity. It also has granulated powder 12a also has a low remanent magnetization and can be filled easily and uniformly into a cavity without causing bridging. In addition, these are primary particles 10a bound (coupled) only by means of the magnetic agglomeration force. Therefore, as on the left side of the 1 (a) shown the granulated powder 12a easy to primary particles 10a be disassembled in the desired manner by applying an aligning magnetic field (e.g. from about 0.1 T to about 0.8 T). As a result, the primary particles 10a aligned with the applied magnetic field. Because the granulated powder 12a no granu contains, the amount of carbon contained in the sintered body never increases. A magnet made by magnetizing a sintered body from this granulated powder 12a has essentially the same magnetic properties as a magnet made without granulating the powder material (with a remanent magnetization of substantially zero). That is, by using the granulated powder according to the preferred embodiment of the present invention, the fluidity and the pressability can be improved without deteriorating the magnetic properties. If necessary, it is of course also possible to add a granulating agent, for example to increase the strength of the compact. Since such a granulating agent as an additional agent is used, the granulating agent need not have a strong binding force. The amount and type of the granulating agent can be selected so that the magnetic properties are not impaired.

In contrast, the granulated powder 12b which is due to the binding of the primary particles 10b the powder material with a granulating agent 14 has been obtained, even when an aligning magnetic field is applied, as in 1 (b) shown, are not sufficiently crushed (disassembled). As a result, the magnetic properties of the resulting sintered magnet are deteriorated (worse). Compared to a magnet obtained without granulating the powder material, the remanent magnetization of this sintered magnet can decrease by about 1% to about 10%. It should be noted that the arrows are from the primary particles 10b of in 1 (b) granulated powder shown 12b are omitted because the particles 10b have no remanent magnetization.

If a granular powder 12c by binding and fixing the primary particles 10c together with a granulating agent 14 has been produced with simultaneous alignment of the primary particles 10c under the influence of a static magnetic field, as in 1 (c) shown, the impairment of the magnetic properties can then be minimized, the granulated powder 12c However, it cannot completely become the primary particle 14c be disassembled. Therefore, the remanent magnetization of the resulting sintered magnet decreases by about 1% to several% compared to a magnet that was manufactured without granulating the powder material. In addition, the granulated powder 12c , like in the 1 (c) shown schematically, elongated in the directions of the magnetic poles, which is disadvantageous for the fluidity. Because the granulated powder 12c The granulated powder also has a relatively high remanent magnetization 12c Bridge bonds and it cannot be filled into a cavity unless it is demagnetized first.

In contrast, the granular powder 12a The preferred embodiment of the present invention is almost spherical in shape, has too little residual magnetization to require demagnetization, and can be easily and uniformly filled into a cavity. Therefore, a so-called "measurement and filling method" can be used, in which a predetermined mass of a granulated powder is determined beforehand and then filled into a cavity. As described above, the granulated powder 12a the preferred embodiment of the present invention have excellent fluidity and void fillability, and this can contribute to the manufacture of a sintered magnet without substantially deteriorating (deteriorating) the magnetic properties.

On granulated powder according to a preferred embodiment The invention is obtained by a granulation process which Stages include: allowing kinetic energy to act on the Particles of a powder material with a remanent magnetization and allowing the particles to grow under the influence of a tumbling effect, the one supplied by the kinetic energy is generated. If necessary, a granulating agent be added if necessary.

In a method for producing a granulated powder according to a preferred embodiment of the present invention, the step of generating a remanent magnetization in the powder material can be carried out either before the powder material has been filled into the container of a granulating device (ie into a granulating container) or after powder material has been made (or filled) in the container. The primary particles 10a of the granulated powder 12a However, this preferred embodiment is tied together (coupled) under the influence of a magnetic agglomeration force generated by the remanent magnetization. Therefore, the granulated powder 12a disassembled when applying an external magnetic field. For this reason, the particles are allowed to grow at a substantially zero magnetic field. This is in contrast to the process for producing the granulated powder 12c , as in 1 (c) shown, in which a magnetic field must be continuously applied to the primary particles 10c align until the granulated powder 12 finally with the granulating agent 14 has been fixed. The expression "substantially zero magnetic field" as used herein means a magnetic field which is weak enough to obtain a granulated powder, a closed magnetic circuit being formed by the remanent magnetization of the powder and no influence to have the remanent magnetization of the powder.

The magnetic field to be applied to a remanent magnetization can generate any of various magnetic fields his. Because the primary particles may have a low remanent magnetization preferably a demagnetizing alternating field is used. The magnetic field to generate a remanent magnetization must however, it should not be such a demagnetizing alternating field, but can also be a uniform demagnetizing field, another type of pulse magnetic field or be a static magnetic field.

It should be noted that even after a residual magnetization is generated, a powder material with a low coercive force may lose the magnetization and shape of the granulated powder before the finished granulated powder is obtained. For this reason, the powder material preferably has a relatively high coercive force. Particularly when the value of the coercive force of a powder material which has been filled in a container so that it has a tap density of 2.0 g / cm ^{3 is} measured by a BH tracer as the apparent coercive force of the powder material the powder material preferably has a coercive force or field strength of at least 70 kA / m, particularly preferably of 80 kA / m or more. For example, an alloy based on R-Fe-B preferably contains at least 2% by mass of Dy and at least 1% by mass of Tb or at least 1% by mass of Dy and Tb in combination.

in the In terms of fluidity and the pressability is the R-Fe-B-based alloy powder that should be pressed and compressed, preferably only from the like granular powder prepared as described above. alternative can also be a mixture of the granulated powder and the powder material (i.e. H. the powder from primary particles) be used. However, since the percentage of powder material increases, the fluidity decreases from. To flow with sufficient effectiveness to improve by granulating, the alloy powder preferably consists essentially only of the granulated powder. If the mixture of the powder material and the granulated powder is also used surface the powder material particles are preferably coated with a lubricant. By coating the surface of the primary particles with a lubricant, the flowability of the R-Fe-B-based powder can be improved and its oxidation can be prevented at the same time. Moreover can when the powder is pressed in a magnetic field also the powder particles be more easily aligned. It should be noted that not only a powder consisting essentially of a rare earth alloy (possibly with a surface oxide layer), but also a powder that is a granulating agent and / or a lubricant and contains the rare earth alloy powder and subjected to a compression process has been referred to herein as "rare earth alloy powder".

below describes a method for producing a magnet from a sintered body an R-Fe-B based alloy according to a preferred embodiment of the present invention described step by step.

First, flakes are made from an R-Fe-B-based alloy using a tape casting process (see, e.g., U.S. Patent No. 5 383 978 ). Specifically, an R-Fe-B-based alloy made by a known method is melted by an induction heating method to obtain a molten alloy. The R-Fe-B-based alloy can also be that described in U.S. Patent No. 4,770,723 or in U.S. Patent No. 4,792,368 have the composition described. In a typical composition of the R-Fe-B-based rare earth alloy, Nd or Pr is typically used as R (rare earth element), and part of the Fe can be replaced by a transition metal (such as Co) and part of B can be replaced by C.

This molten alloy is held at 1,350 ° C and then rapidly quenched on a single roll under conditions including a roll circumferential speed of about 1 m / s, a cooling rate of 500 ° C / s, and a cooling to below 200 ° C, whereby alloy flakes with a thickness of 0.3 mm are obtained. A coarse alloy powder is obtained by decrepitation of these alloy flakes using a hydrogen inclusion process. Then this coarse alloy powder is finely pulverized by means of a jet mill within a nitrogen gas atmosphere, whereby an alloy powder (ie powder material) with an average particle size of 1.5 μm is obtained to 6 microns and a specific surface area of about 0.45 m ² / g to about 0.55 m ² / g, measured by the BET method. This powder material has a true density of 7.5 g / cm ³ .

After that becomes a remanent magnetization in the thus obtained Powder material generated. In this example, a demagnetizing Alternating field with a peak magnetic field of 1.0 T applied to it.

Then will granulated the powder material with the remanent magnetization. In this example, a fluid bed granulation technique is used. With the fluid bed or fluidized bed granulation technology can be used with a granulated powder a quasi-spherical one Shape and be obtained with sufficient hardness. If that granulated powder having such an almost spherical shape can be a excellent fluidity and excellent pressability can be achieved. Besides, is the hardness the granulated powder can be changed with the granulating agent. However, there are disadvantages if the granulated powder is too hard is or is too soft, as described above.

A known granulating device 20 for granulating a powder using the fluidized bed or fluidized bed granulation process is shown in US Pat 2 schematically explained. The pelletizer 20 includes a fan blower 21 , a temperature and humidity control device 22 , a liquid container 23 , Changeover valves 24 and a reversing fan 26 , As a pelletizer 20 a swing processor from Fuji Paudal Co., Ltd. is preferably used.

First, there is normal fluidization in the liquid container 23 performed using an air flow through the fan blower 21 is produced. in this case the air flow is at a positive pressure in the direction indicated by the solid arrows (fluidization process stage). After that, when the changeover valves 24 be turned on, the direction of air flow through the reversing fan 26 redirected in the direction indicated by the dashed arrows (consolidation process stage). In this consolidation process stage, a powder layer is formed and pressed and the hardness of the granulated powder is increased by the downward air flow. In the fluidization process stage, on the other hand, the powder layer formed in the consolidation process stage is broken down (comminuted) by the upward-directed air flow and a granulated powder with an almost spherical shape is produced under the influence of the grinding action of the fluidized air flow. The changeover valves 24 can be switched on repeatedly. The hardness of the granulated powder can be adjusted by controlling the air volume and repeating the cycles. The average particle size of the granulated powder can also be adjusted by controlling the duration of the granulation process.

In the conventional fluid bed granulation process, the step of fluidizing a powder with an upward gas flow in a container (also referred to as "orientation of the powder flow") (ie the fluidization process step) and the step of pressing a layer of powder through a downward gas flow ( ie the consolidation process stage) carried out separately. For example, the one disclosed in Japanese Patent No. 3,019,953 shown fluidization and pressing device (cf. 3 ) constructed in such a way that a gas stream for carrying out the fluidization process stage (here referred to as "first gas stream") is switched over to a gas stream for carrying out the consolidation process stage (here called "second gas stream") or vice versa. In this way, the conventional device cannot generate these two gas streams simultaneously within the container.

The Inventors of the present invention have now found and through Tests confirmed that a granular rare earth alloy powder to more effective Can be produced by introducing the first gas stream to carry out the fluidization process stage simultaneously with the introduction of the second gas flow for implementation the consolidation process stage in the container.

This is believed to be due to the rare earth alloy having a relatively high absolute specific gravity of 7.5 g / cm ³ and / or the granulated powder being used by using a relatively weak force such as e.g. B. is generated by remanent magnetization. This resulted from the experimental results that, if no binder was used, the granular powder production yield decreased unless the consolidation process step was performed after the first and second gas streams were present within the same container, but then If a binder was used, no difference between the conventional and the inventive method was found. It is not entirely clear why the granulated powder can be made more effectively when the first and second gas streams are present at the same time.

A method and an apparatus for producing a granulated powder according to a preferred embodiment of the invention will be described below with reference to FIG 3 and 4 described in more detail.

In the 3 becomes a configuration for a device 100 for producing a granulated powder in a schematic form, which can be used effectively in a method for producing a granulated powder according to a preferred embodiment of the present invention. The 4 (a) and 4 (b) FIG. 12 are diagrams schematically showing how the (flow rates of) gas flows in a container change (with the lapse of time) in a method for producing a granular powder according to a preferred embodiment of the present invention.

The in the 3 shown device 100 for the production of the granulated powder comprises a container (fluidization container) 30 , a first channel 40 (a) with the container 30 communicates and the first upward gas stream in the container 30 can generate, and a second channel 50 (b), also with the container 30 communicates and the second downward gas stream in the container 30 can generate. The first channel 40 (a) and the second channel 50 (b) stand independently of each other with the container 30 in connection. It should be noted that the reference numbers 40 and 50 are mainly used to represent the physical structures of the first and second channels, while reference numerals a and b are mainly used to represent the gas flow paths of the first and second channels.

The container 30 has such a structure that it is a vessel 62 on the bottom, which is filled with a rare earth alloy powder. The bottom plate (or base plate) 62b of the vessel 62 is permeable to air and can consist, for example, of a net (grid) or a fabric. In terms of work efficiency, such a vessel 62 preferably used. However, any other structure can be used as long as the container 30 includes the air-permeable base plate.

The rare earth alloy powder that is on the bottom plate 62b of the vessel 62 is arranged by the first gas flow coming from below the bottom plate 62b flows in the upward direction, the energy required to fluidize it. In this case, the rare earth alloy powder is granulated under a substantially zero magnetic field by taking advantage of the agglomeration force generated by the remanent magnetization of the rare earth alloy powder and by a tumbling effect generated by the kinetic energy the powder has been supplied by the first gas stream. There is also a layer of powder on the base plate 62b formed as a result of the weight of the powder itself and / or the second gas stream, and then compressed by the second gas stream, thereby consolidating the powder.

The first channel 40 includes a temperature control device 42 , a blower (e.g. a fan blower) 44 and a pipeline 46 and it stands by means of the valves 47 and 48 with the container 30 in connection or is coupled to it, which defines the first channel in which the gas is circulated within the container 30 (cf. the in the 3 arrows A1 and A2). In order to minimize the oxidation of the rare earth alloy powder, an inert gas (e.g. an inert gas or nitrogen gas) is preferably used. Nitrogen gas is used in this example. It should be noted that the volume fraction of the oxygen gas compared to the total gas is preferably set to 0.1% or less.

If then the rare earth alloy powder has an excessively high temperature also take the coercive force or field strength and the agglomeration force of the powder so strong that not easily a granulated powder can be manufactured. To avoid this situation and / or to minimize the oxidation of the rare earth alloy powder, the gas temperature is preferably set to within the range of 10 ° C up to 40 ° C, particularly preferred is within the range of 20 ° C to 30 ° C. If necessary, a moisture control device be provided for removing water from the gas if so is required.

The blower 44 generates the first gas stream from the gas, its temperature by the temperature control device 42 has been discontinued. The flow rate of the inside of the container 30 The first gas flow generated is controlled by adjusting the output of the fan 44 and / or the degree of opening of the valve 47 ,

The second channel 50 includes a buffer tank 52 and a pipeline 36 and stands by means of the valves 57 and 58 with the container 30 in communication (or is coupled to it), thereby defining the second channel b, which is the gas within the vessel 30 in the cycle (see the in the 3 arrows B1 and B2 shown). It should be noted that the buffer tank 50 with a main pipeline (e.g. a factory nitrogen gas pipeline) 54 via a controller 53 communicates. That of the source pipeline 34 supplied nitrogen gas can have a pressure of about 7 kg / cm ² , which is regulated by a regulator 33 is reduced to several kg / cm ² . The flow rate of the gas flow generated within the vessel is controlled by adjusting the degree of opening of the valves 57 and 58 ,

Both ends of the first channel 40 and both ends of the second channel 50 all stand with the container 30 connected so that the gas flow path is essentially closed. Therefore, conditions (for example, temperature and moisture content) of the nitrogen gas in the container 30 can be effectively controlled, and the consumption of nitrogen gas can also be reduced. Even if the system is completely closed, it would be difficult to control the gas flows. For this reason, a configuration is preferably adopted for discharging the nitrogen gas from the container 30 with a given resistance by connecting an exhaust pipe 34 with the container 30 by means of a valve 36 , In this case the resistance of the exhaust pipe 64 preferably set so that the pressure inside the container 30 is kept higher than the pressure outside the container 30 (ie atmospheric pressure), at least during operation.

In addition, the rare earth alloy powder is easily oxidized. Therefore, if the temperature of the rare earth alloy powder rises abnormally, the rare earth alloy powder may even explode. For this reason it is inside the container 30 preferably a thermometer 38 arranged for measuring the temperature inside the container. In addition, a control circuit is preferably provided to operate at least the blower 44 to stop when the temperature inside the container 30 exceeds a predetermined value. If necessary, the valves 47 . 48 . 57 . 58 and 66 Solenoid valves can be and they can be controlled so that they are closed when the temperature inside the container 30 exceeds the specified temperature. According to the results of the various tests, if an R-Fe-B-based alloy is used, it is very likely that rapid oxidation (possibly under ignition or explosion) will occur at a temperature above 50 ° C. For this reason, the temperature at which the stop operation starts is preferably set at 50 ° C.

In the container 30 the inner diameter at and around the bottom section differs for the receptacle of the vessel 62 from that of the body portion located above the bottom portion. As in 3 is shown, the inner diameter D1 of the bottom portion of the container 30 smaller than the inner diameter D2 of the body portion thereof. The closer this is to the body section, the larger the inside diameter. If a container 30 is used with such a structure, the flow rate of the first gas flow through the first channel increases 40 in the container 30 is generated in the upward direction. Therefore, the powder fluidized by the first gas stream can effectively fall down. The bottom portion, which has an inner diameter that is smaller than the inner diameter D2 of the body portion, has a length (or height) that is about 20% of the total length of the vessel 30 accounts. The minimum inside diameter D1 of the bottom section (ie the inside diameter of the section on which the bottom plate 62b arranged) can, for example, make up about 50% of D2.

The device 100 a device for producing a granulated powder may also be used 60 to generate a magnetic field which have a magnetic field applied to the vessel 62 filled rare earth metal alloy powder can create. The facility 60 that can generate a magnetic field can be an electromagnet that comprises a coil and a yoke and is preferably able to generate a demagnetizing alternating field. If a rare earth alloy powder with a remanent magnetization, the outside of the container 30 has been generated, then the device can 60 , which creates a magnetic field, are naturally omitted.

The following will refer to the 4 (a) and 4 (b) described how the gas flows in the container 30 change their states in the process for producing a granulated powder according to a preferred embodiment of the present invention. In particular, the 4 (a) a series of procedural stages (corresponding to one cycle) from the point of departure of the operation, during the 4 (b) shows a series of process stages (corresponding to a cycle) which comprises a comminution process stage.

First, referring to the 4 (a) described what the state of the gas flow in the container 30 is after the vessel 62 , which is filled with a rare earth metal alloy powder with remanent magnetization, in a predetermined position in the device 100 has been used.

If the vessel 62 is used, the flow rate a _{0 of} the first gas stream a and the flow rate b _{0 of} the second gas stream b are both zero. Then the temperature controller 42 and the blower 44 turned on and the valves 47 and 48 are opened, creating the first gas stream a in the container 30 is produced. The flow rate of the first gas stream a gradually increases until it soon reaches an equilibrium flow rate a ₁ . In such a state, the powder is granulated under the agglomeration force generated by the remanent magnetization while at the same time causing a tumbling effect in the container 30 is exposed. In the meantime, part of the powder is around the center of the container 30 is arranged around (including the particles that are to be granulated) on the first gas stream a, against the force of gravity, while another part of the powder that flows around the inner wall of the container 30 is arranged around where the flow rate is low, due to its own weight falls down.

If the flow rate of the first gas stream a is kept substantially constant for a predetermined period of time (for example about 20 min), the valves become 57 and 58 opened to start the generation of the second gas stream b (whose flow velocity at the starting point is b ₁ ). The flow rate of the second gas stream b gradually increases. However, before the flow rate of the second gas stream b has reached its equilibrium flow rate b ₂ , the flow rate of the first gas stream a begins to decrease (whose flow rate at the starting point is a ₂ ). That is, there is a period of time within which the flow rate of the first gas stream a decreases, while that of the second gas stream b increases (ie the period between a ₂ and b ₂ , as in FIG 4 (a) ) Shown. If you have the first gas stream a and the second gas stream b in the same container 30 maintained in this manner for a period of time, a granulated rare earth alloy powder can be produced more effectively. The reason is not entirely clear. It appears that when the first gas stream a is stopped abruptly or when the flow rates of the second gas stream b is too much higher than that of the first gas stream a, the granulated powder falls so quickly that the granulated powder falls into pieces as a result of the impact breaks. In addition, when the second gas stream b, the production of which is started after the first gas stream a has completely stopped, becomes a negative pressure in the container 30 generated, which makes it more difficult to control the pressure, which is not advantageous.

As described above, when the flow rate of the second gas stream b is gradually increased while the flow rate of the first gas stream a is gradually decreasing, the granulated powder is never broken into pieces as a result of the impact when it falls on the floor plate 62 strikes, but a powder layer is formed on it. The powder layer is then compressed and consolidated by the second gas stream b. As a result of this consolidation process, the hardness of the granulated powder increases.

By repeating the in 4 (a) cycle shown, a granulated powder with sufficient hardness can be obtained. However, it should be pointed out here that the flow velocity of the first gas stream a at the starting point of the second cycle need not have the value zero (a ₀ ) in the subsequent cycles, as in FIG 4 (a) shown, but the flow velocity a ₃ at the end point of in 4 (a) cycle shown may be the same.

However, only by repeating the cycle as in 4 (a) shown, the powder layer on the bottom plate 62b has been compressed, cannot be crushed sufficiently, and particles having an excessively large particle size can be formed. Therefore, in order to perform the crushing of the powder layer with higher certainty, the in 4 (b) cycle shown carried out preferably.

Below are the process steps that are carried out from point b ₁ ', as in 4 (b) shown, described. In the example below, the process steps at point b ₁ as described in 4 (a) is to be carried out, also carried out up to this point b ₁ ', as in 4 (b) shown, and then those in the 4 (b) process steps shown performed.

The generation of the second gas stream b is started (at a flow velocity b ₁ 'at the starting point), as described above. Before the flow rate of the second gas stream b has reached its equilibrium flow rate b ₂ ', the flow rate of the first gas flow a (from a flow velocity a ₂ 'at the starting point). After that, the valves 47 and 48 closed to the first gas stream a (for α min between times a ₃ 'and a ₄ ', as in 4 (a) shown) to keep stopped. If the blower 44 has been operated in the meantime, then a section of the pipeline 46 between the blower 44 and the valve 47 an increased gas pressure. In other words, the valve 47 should remain closed until a predetermined pressure for crushing the powder layer can be achieved. Then the second gas flow b is stopped by closing the valves 57 and 58 (at the point b ₀ 'as in 4 (b) shown) and the first gas stream a is generated by opening the valves 47 and 48 (at point a ₀ 'as in 4 (b) ) Shown. In this case, the flow rate a ₀ 'of the first gas stream a exceeds that in the container 30 the equilibrium flow rate a ₁ (= a ₂ ) of the first gas stream a, as in 4 (a) shown, which makes it possible to effectively shred the powder layer. In order to produce the tumbling effect, the flow velocity of the first gas stream a is generally kept essentially constant (a ₁ = a ₂ ), as in 4 (a) shown, but it can also be variable. In this case, the flow rate of the first gas stream a for comminuting the powder layer is preferably higher than the average flow rate of the first gas stream a in order to produce the tumbling effect.

In the example described above, the first gas stream a with the flow rate a ₀ 'is generated by actuating the valves 57 and 58 , Alternatively, the flow rate of the first gas stream a can also be adjusted by controlling the blowing capacity of the blower 44 , Blowing capacity control can also be combined with valve control. It should be noted that the flow velocities a ₁ 'and a ₂ ', as in 4 (b) shown, the flow velocities a ₁ and a ₂ can be the same as in 4 (a) shown.

When the size of a granulated powder to be formed by using the remanent magnetization has reached a certain value, a closed magnetic circuit is created and the magnetic attraction between the particles of the granulated powder decreases. In this case the is in 4 (b) shown shredding cycle is no longer required. Therefore, in a method in which a predetermined granular powder can be obtained by repeatedly performing the in 4 (a) shown basic cycle and in 4 (b) shown crushing cycle for a total of 30 cycles, for example 5 to 10 crushing cycles preferably contained in the first 20 cycles.

It it should be noted that if such a powder material is used with a retentive magnetization, a given one granulated powder can be obtained in a shorter time (e.g. in half time) than in a situation where a powder material without remanent magnetization is used. It is believed that this is because that if such a powder material with a remanent Magnetization is used, the seed to form the granulated powder is easily generated by the magnetic agglomeration force between the primary particles.

The Granulated powder preferably has an average particle size of 0.05 mm to 3.0 mm. A normal granulated powder contains a few primary and a very big one Number of tertiary and other particles higher Order. The average particle size of the secondary particles can be viewed as being essentially the middle one Particle size of the granulated Powder represents. In this example, the average particle size of the secondary particles, which is determined by a microscope, as the average particle size of the granulated Powder used. If the granulated powder has an average particle size of <0.05 mm, then can not flow so significantly improved and a uniform compact with one sufficient density can hardly be obtained. However, if the granulated powder has an average particle size of> 3 mm, then takes the room filling capacity from and it is also a uniform one Hardly obtainable compact with a sufficient density. The granular Powder particularly preferably has an average particle size of 0.1 mm to 2.0 mm.

After that a compact is produced by pressing and compacting the granulated powder thus obtained. In this example a compact is made only from the granulated powder. The compression process can be carried out using a known pressing device carried out become. As a rule, a uniaxial pressing device is used for pressing a powder into a mold cavity (or in a form hole) used with upper and lower stamps. The granulated powder can be transported in portions with a very airtight container be filled, for example, with a nitrogen gas or is supplied with a nitrogen gas.

The granulated powder is filled into the mold cavity of a uniaxial press. The The step of filling the granulated powder into the cavity can be carried out either with a sieve or with a loading box as described in Japanese Patent Gazette for Opposition No. 59-40560 , in Japanese Patent Laid-Open Publication No. 10-58198 , in Japanese Utility Model Publication No. 63-110521 or in Japanese Laid-Open Publication No. 2000-248 301 described. The processes described in these documents are collectively referred to here as "drop-off processes".

In particular in the production of a small compact, it is granulated Powder preferably filled into the cavity in such an amount that corresponds to the volume of the cavity. For example a loading box with an opening on the ground above the cavity to be transported so the granulated powder falling under the influence of gravity (i.e. by itself) to let, and then the excess of the granulated powder, which over overflows the cavity, stripped. In this way, a given amount of granulated powder be filled in relatively evenly. It is natural possible, to determine the granulated powder separately and then, for example fill with a funnel into the cavity.

After this the cavity was filled with the granulated powder in this way the upper punch of the uniaxial press device is lowered, around the cavity opening to close. Then an aligning magnetic field is applied to it, causing the granulated powder to primary particles breaks up and the primary particles aligned with the applied magnetic field. The granulated powder this preferred embodiment The present invention can be performed as intended with a relatively weak one magnetic field from 0.1 T to 0.8 T can be broken down into primary particles. Around however, it will achieve a sufficient degree of alignment preferably a magnetic field from about 0.5 T to about 1.5 T created. The direction of the magnetic field can, for example run perpendicular to the pressing direction. The powder becomes uniaxial between the upper and lower stamps under a pressure of, for example 98 MPa pressed in this way with a magnetic field applied. As a result, a compact with a relative density (i.e. with a relationship between the pressing density and the true density) from 0.5 to 0.7 be preserved. If necessary, the direction of the magnetic Field run parallel to the pressing direction.

After that the resulting compact is at a temperature of about 1000 ° C to about 1180 ° C about 1 h to about 6 h within a vacuum or in an inert the atmosphere sintered. The granulated powder of this preferred embodiment contains either at all no granulating agent or such a small amount of granulating agent, that it is essentially removable as a result of the sintering process. There is thus no need for a separate binder removal process provided. It should be noted that a conventional typical binder removal process at one temperature of about 200 ° C up to about 800 ° C for about 3 hours to about 6 hours within an inert atmosphere at one pressure of about 2 Pa becomes.

After that becomes the resulting sintered body an aging treatment at a temperature of about 450 ° C to about 800 ° C for about 1 h to about 8 h, resulting in a sintered magnet based on R-Fe-B receives. Subsequently a sintered magnet based on R-Fe-B is finished as the end product Magnetize it at any stage.

According to the invention granulated powder with excellent flowability and pressability as described above. The granular Powder can be extremely high uniform filled into the cavity with a minimal fluctuation in the filling quantity. As a result, the Mass and dimensions of those obtained by the pressing process Pressings only slightly Variations. There is hardly any cracking or cracking in the pellets Chipping on.

Also be in the granulated powder according to this preferred embodiment the primary particles held together essentially by the magnetic agglomeration force, generated by the remanent magnetization. Therefore by applying an aligning magnetic field to the granulated Powder this in the desired one Scope to primary particles be disassembled. The degree of alignment of the primary particles therefore never decreases. Furthermore, impairment can also occur of the magnetic properties that could occur if the carbon of the granulating agent would remain in the sintered body. As a result, a sintered magnet with excellent magnetic Properties are obtained. As a result, according to the invention, a qualitative high-quality sintered magnet made of an alloy based on R-Fe-B high productivity getting produced.

Examples

The The present invention is described in more detail with reference to the following examples.

An R-Fe-B-based alloy powder was manufactured in the following manner: a molten alloy was manufactured by using a ferroboron alloy containing electrolytic iron with a purity of 99.9% and using 19. 8 mass percent of B and Nd and Dy with a purity of 99.7% or more as the respective raw materials. From this molten alloy, flakes were made from an R-Fe-B-based alloy using a tape casting method, which had a composition comprising 30.0% by mass of Nd, 5.0% by mass of Dy, 64.0% by mass of Fe and 1.0 Mass percent B contained. These alloy flakes were finely pulverized using a jet mill in an inert gas (e.g., in N ₂ gas with a gas pressure of 58.8 MPa), whereby a powder material with an average particle size of 3 μm was obtained.

After that there was a remanent magnetization in the powder material of this specific example generated by applying a demagnetizing Alternating field (with a peak value of the applied magnetic Field of 1.0 T).

Then, a granulated powder was produced by using a fluid bed granulation method (using, for example, a swing processor manufactured by Fuji Paudal Co., Ltd.). For the production of granulated powders according to Examples Nos. 2 and 3 and Comparative Examples Nos. 2 and 3, polybdenum and isoparaffin were used as the granulating agent, as described by the applicant of the present application in Japanese Patent Application No. 2001 to 96572 described. In each of the specific examples of the present invention and in each of the comparative examples, the various conditions were defined so that the resulting granulated powder had an average particle size of 0.5 mm. The granulated powder thus obtained had a residual magnetization of about 0.2 mT. In Examples Nos. 1, 2 and 3, the granulation treatment step took about 15 minutes. In Comparative Examples Nos. 2 and 3, on the other hand, it took about 30 minutes to complete the granulation process step. It should be noted that the powder material (to which no magnetic field was applied) as obtained was used in Comparative Example No. 1 without being granulated. The following table 1 summarizes the conditions under which the powders to be pressed were produced in Examples Nos. 1, 2 and 3 and in Comparative Examples Nos. 1, 2 and 3. Table 1

Table 1 also shows the rest angles of the respective powders to be pressed. A powder with a large angle of repose has poor fluidity. The smaller the angle of repose, the better the fluidity. In Comparative Example No. 1, in which the powder material was not granulated, the rest angle was up to about 52 ° and the fluidity was poor. In contrast, in each of Examples Nos. 1, 2 and 3 and Comparative Examples Nos. 2 and 3 in which the powders were granulated, the angle of repose decreased to less than 50 °. Among other things, the powders to be pressed according to Examples Nos. 1 and 2 had smaller angles of repose and had better fluidity than the powder to be pressed, which is Comparative Example No. 2 (to which 1% by mass of granulating agent was added). The This means that it can be seen that by using the remanent magnetization, the fluidity can be improved even if a smaller amount of granulating agent than the conventional amount is added. It should be noted that in Example No. 3 and Comparative Example No. 3 in which the granulating agent was added in an amount of 2% by mass, no difference in the fluidity was found.

each the powder to be pressed specified in Table 1 was put into a Cavity with a length of 20 mm, a width of 15 mm and a depth of 10 mm filled under Application of a method in which a loading box as above was used, and then uniaxially pressed and compressed (under a pressure of 98 MPa and with the application of a aligning magnetic field perpendicular to the pressing direction of 0.8 T). This filling and compression press stages were under the same conditions for all examples according to the invention and comparative examples. It should be noted that compacts with different densities (i.e. green poems) have been preserved with changing Press conditions.

The Fluctuation (%) in terms of mass and fluctuation (σ) in relation to on the filling density between the resulting compacts were used for Example No. 1 and Comparative Example No. 1 estimated. The fluctuation in terms of mass between the compacts was calculated according to the equation {(maximum mass - minimum mass) / average Mass (n = 50)} × 100 (%).

Also poses the fluctuation (σ) in terms of filling density is the standard deviation of the mass distribution of 50 compacts. In Example 1, the variation in mass was between the compacts about 5% and was therefore significantly lower than that Mass variation of about 15% in the comparative example No. 1. This tendency was also observed with the fluctuation (σ) in relation on the filling density. In particular, the fluctuation (σ) was in relation to the filling density in Comparative Example No. 1 about 0.33, while the fluctuation (σ) related on the filling density in Example No. 1 was only about 0.18. It can be seen from this that fluidity through Granulation was improved. The pressability was of course the same improved by granulating. The percentage of cracking or chipping found in the compacts of Example No. 1 was much lower than in Comparative Example No. 9. This Effects obtained by granulating were also seen in the other examples approved.

Everyone the resulting compacts were sintered in an Ar atmosphere at 1060 ° C for about 4 hours then at 600 ° C for 1 h subjected to an aging treatment, thereby obtaining a sintered body has been. Then this sintered body was further magnetized 2 387 kA / m to achieve a sintered magnet. For each of the examples according to the present Invention and the comparative examples, 50 samples were obtained.

The 5 shows the remanence B _r (T) of the resulting sintered magnets. How out 5 there was practically no difference between the Br of Example No. 1 (shown in 5 by filled circles) and the Br of Comparative Example No. 1 (in the 5 indicated by empty circles). The sintered magnet thus had excellent magnetic properties. The Br of Examples Nos. 2 and 3, to which a granulating agent had been added, was approximately the same as Comparative Example No. 2 or 3, to which the same amount of granulating agent was added, but using a powder material without residual magnetization. Even when granulating a powder by using the remanent magnetization, the granulating agent was preferably added in the smallest possible amount.

How given above was obtained by producing a granular one Powder using the magnetic agglomeration force that was generated by the remanent magnetization of the primary particles themselves then when the amount of the granulating agent to be added is reduced was compared to the situation where a granulated powder was produced using the coupling force of the granulating agent alone achieved at least the same level of fluidity. Therefore a sintered magnet that has better magnetic properties, with at least the same productivity as a conventional sintered magnet. When a granulated powder is made is exploited only by the remanent magnetization of the primary particles, can also an impairment the magnetic properties are essentially eliminated.

Examples Nos. 4 to 6 in which a granulated powder was produced using the manufacturing apparatus are described below 100 , The same powder material as in Examples 1 to 3 was also used.

The container 30 had an inner diameter D2 of 300 mm and a volume of about 7 × 10 ⁴ cm ³ . In the 4 (a) and 4 (b) The flow rates a ₁ = a ₂ = a ₁ '= a ₂ ' were approximately 1 m ³ / min, the flow rates a ₀ 'were approximately 2.0 m ³ / min and the flow rates b ₂ = b ₃ = b ₂ ' = b ₃ 'was approximately 0.75 m ³ / min. About 5 kg of the rare earth alloy powder was charged and the temperature of the nitrogen gas was adjusted to about 30 ° C.

Polybdenum and isoparaffin were used as granulating agents for the production of granulated powders, which represent Examples Nos. 5 and 6, as described by the applicant of the present application in Japanese Patent Application No. 2001 to 96572 and described as in Examples Nos. 2 and 3. In Examples Nos. 5 and 6, the various conditions were also defined so that the granulated powder had an average particle size of 0.5 mm. The resulting granulated powder had a residual magnetization of about 0.2 mT. In Examples Nos. 4 to 6, the granulation process was carried out for about 15 minutes. Table 2 below summarizes the conditions under which the powders to be pressed were produced, and the angles of repose for examples Nos. 4 to 6 are also given. Table 2

As can be seen from Table 2, the powders to be pressed, which represent examples Nos. 4 and 5, had even smaller rest angles than the powders to be pressed, which represent examples Nos. 1 and 2. By using the manufacturing device 100 the flowability was thus further improved. That by using the manufacturing device 10 The advantages achieved are, however, not so much reduced angles of rest as an improvement in the stability (or reproducibility) of the granulation process. For example, it was found that compared to the fluctuations in the angle of rest in the resulting granulated powders, the angle of rest in Example No. 1 varied from 45 ° to 49 °, while the angle of rest in Example No. 4 varied much less, that is, from 44 ° to 45 °. If the in the 2 known pelletizer, or that disclosed in Japanese Patent Publication No. 3,019,953 (see. 3 pelletizer described in this publication), the step of whirling the powder onto an upward rising gas stream in the container (ie a swirling step) and the step of compressing the powder layer with a downward gas stream (ie a consolidation step) ) as two separate process steps. However, the inventors of the present invention have found that a granulated powder of a rare earth alloy can be produced more effectively by using the manufacturing device 100 so that the first gas stream to achieve the fluidization process stage and the second gas stream to perform the consolidation process stage were present in the same container at the same time. Among other things, significant effects were obtained when no granulating agents were used, as shown in Example No. 4.

Under Use of the powder to be pressed, which is the example No. 4 represent to 6 in Table 2, compacts were prepared as in Example No. 1 and the fluctuation in terms of mass (%) and the variation in terms of filling density (σ) between these compacts were evaluated. The pellets of the example No. 4 showed a mass fluctuation of about 4%, which was even less was like that in Example No. 1. The same tendency was also determined for the variation with respect to the filling density (σ). In particular could the variation in fill density (σ) of the Example No. 4 can be improved to 0.16. The mass fluctuations (%) and the filling density fluctuations (σ) the Compacts, which represent Examples Nos. 5 and 6, were at least comparable to those of Example No. 2 and 3.

Each of the compacts representing Example Nos. 4 to 6 was sintered in an Ar atmosphere at 1060 ° C. for about 4 hours, and then subjected to an aging treatment at 600 ° C. for 1 hour, whereby a sintered body was obtained. Thereafter, this sintered body was further magnetized at 2,387 kA / m to produce a sintered magnet. 50 samples were obtained for each of Example Nos. 4 to 6. The sintered magnets representing Examples Nos. 4, 5 and 6 had remanences B _r (T) which were approximately the same as those of Examples Nos. 1, 2 and 3. By using the manufacturing device 100 granulated powder can be produced in a more constant manner than by the conventional method. Accordingly, a granulated powder with a smaller amount of granulating agent than the conventional method (or even without using granulating agent) can be obtained. As a result, a sintered magnet can be obtained which has better magnetic properties (e.g. a better remanence B _r ) than conventional sintered magnets.

industrial applicability

The The present invention relates to a method for producing a granulated rare earth alloy powder that has good fluidity and has good pressability, and it enables the production of a Magnets with excellent magnetic properties. The invention also relates to a method for producing a good quality Rare earth alloy sintered body with high productivity Use of such a granulated powder.

According to the invention Fluidity and improves the pressability of a rare earth alloy powder without affecting the magnetic properties (to deteriorate). This way, even a sintered magnet, which is too complicated to be pressed into a certain shape to become and easily compacted and its magnetic Properties to a certain extent in the prior art sacrificed, also improved magnetic properties exhibit. Moreover can shorten the granulation time and the binder removal process can be omitted. As a result, the productivity of rare earth sintered magnets can be increased.

Summary

The invention relates to a method for producing a granulated rare earth alloy powder, which comprises the steps:
Making a rare earth alloy powder; Creating a remanent magnetization in the powder; and granulating the powder by utilizing the agglomeration force generated by the remanent magnetization of the powder. Since the agglomeration force generated by the remanent magnetization is used, the addition of a granulating agent can be omitted.

Claims (28)

Process for producing a granular Rare earth alloy powder, the process comprising the steps of: Production of a rare earth alloy powder; generation residual magnetization in the powder; and Granulate of the powder by exploiting the agglomeration force caused by the remanent magnetization of the powder is generated. The method of claim 1, wherein the step of Granulation one stage of feeding of kinetic energy to the powder particles, the Particles grow under a tumbling effect created by the fed kinetic energy, under a substantially zero magnetic field. The method of claim 1 or 2, the steps includes: Production of the powder with a remanent magnetization in a container; and Exposure to kinetic energy under a magnetic Substantially zero field in the container on the powder particles. A method according to claim 1 or 2, comprising the steps of: preparing the powder in a container; Creating a remanent magnetization in the powder in the container by applying a magnetic field to the powder; and allowing kinetic energy to act on the powder particles with the remanent magnetization under egg a substantially zero magnetic field in the container. A method according to any one of claims 1 to 4, further comprising a Stage of adding a granulating agent to the powder. A method according to any one of claims 1 to 4, further comprising a Step of not adding a granulating agent to the powder. Method according to one of claims 1 to 6, wherein the step the generation of a remanent magnetization in the powder Stage of applying a demagnetizing alternating field includes. A method according to any one of claims 1 to 7, in which the rare earth alloy is an R-Fe-B based alloy that is 2 mass percent or more Dy, 1 mass percent or more Tb or 1 mass percent or more Contains Dy + Tb. A method according to any one of claims 1 to 8, wherein the powder has an average particle size of 1.5 μm to 6 μm. A method according to any one of claims 1 to 9, wherein the granulating step a step of producing a granulated powder with a average particle size 0.05 mm to 3.0 mm. A method of manufacturing a rare earth alloy sintered body the stages include: Production of a Granulated Rare Earth Metal Alloy Powder by the method according to any one of claims 1 to 10; Filling one Cavity with a rare earth alloy powder, which the granulated powder comprises, without applying a demagnetizing magnetic field to the granulated powder; Making one Pellets by pressing the rare earth alloy powder, which comprises the granulated powder, with the application of an aligning powder magnetic field thereon; and Sintering the compact. Granulated rare earth alloy powder, the a rare earth alloy powder with a remanent magnetization and an average particle size of 1.5 μm to 6 μm, wherein the granulated powder has an average particle size of 0.05 mm to 3.0 mm, whereby the powder by means of an agglomeration force, generated by the remanent magnetization, bound (coupled) is. Process for producing a granulated rare earth alloy powder, the process comprising the steps of: (a) Making one Rare earth metal alloy powder with a remanent magnetization in a container by placing the powder on an air permeable base plate; (B) Generation of a first gas stream in the container so that the first gas stream flows up from below the base plate; (c) feeding kinetic energy to the powder particles by means of the first gas stream, to thereby essentially remove the powder under a magnetic field Granulate zero by exploiting the agglomeration force that is generated by the remanent magnetization of the powder, and of a tumbling effect created by the kinetic energy becomes; (d) generating a second gas stream in the container such that the second gas stream flows down from above the base plate; and (E) Forming a powder layer from the powder on the base plate and Compress the powder layer with the second gas stream, at least part of stage (d) and at least part of stage (b) at the same time carried out become. The method of claim 13, wherein the period of time within which stages (d) and (b) are carried out simultaneously, includes a period in which the flow rate of the first Gas flow decreases while that of the second gas stream increases. The method of claim 13 or 14, wherein the step (a) the stages include: filling a rare earth alloy powder without residual magnetization in the container producing residual magnetization in the powder without retentive magnetization that has been filled into the container by application of a magnetic field on the powder. The method of claim 13 or 14, wherein the step (a) the steps include: producing a rare earth alloy powder with a retentive magnetization and filling the powder with a retentive magnetization in the container. A method according to any one of claims 13 to 16, wherein the steps (b), (c), (d) and (e) are repeated several times in the order mentioned carried out become. The method of claim 17, further comprising the Stage includes (f) stopping the first gas stream while simultaneously Generation of the second gas stream and subsequent stopping of the second Gas flow with simultaneous renewed generation of the first gas flow at a flow rate, which is the average flow rate of the first gas stream in step (c), thereby causing the powder layer to which has been formed on the base plate, whereby stage (f) is carried out at least once after stage (e), while steps (b) to (e) are carried out repeatedly. A method according to any one of claims 13 to 18, wherein the rare earth alloy is an alloy based on R-Fe-B. A method according to any one of claims 13 to 19, wherein the powder has an average particle size of 1.5 μm to 6 μm. A method according to any one of claims 13 to 20, wherein the method to form a granulated powder with an average particle size of 0.05 mm to 3.0 mm leads. A method of manufacturing a rare earth alloy sintered body, the the stages include: Production of a Granulated Rare Earth Metal Alloy Powder by the method according to any one of claims 13 to 21; Filling one Cavity with a rare earth alloy powder, which the granulated powder comprises, without applying a demagnetizing magnetic field to the granulated powder; Making one Pellets by pressing the rare earth alloy powder, which comprises the granulated powder, with the application of an aligning powder magnetic field thereon; and Sintering the compact. Device for producing a granulated rare earth alloy powder, which includes: a container, which is a base plate for includes the inclusion of a rare earth alloy powder; one first channel that with the container is connected to generate a first gas stream, which is from below the base plate in the container flows upwards; and a second channel connected to the container for generation of a second gas stream, which from above the base plate in the container flows down, in which the first channel and the second channel are independently connected to the container are. The apparatus of claim 23, further comprising Temperature control device and a blower within the first channel includes. The device of claim 23 or 24, further comprising Buffer tank included within the second channel. Device according to one of claims 23 to 25, further comprising a Control loop includes a thermometer to determine the temperature of the gas in the container includes and the operation of the blower stops at least when the measured temperature reaches a predetermined one Temperature exceeds. Device according to one of claims 23 to 26, in which a positive Maintain pressure within the container will while the device is in operation. Device according to one of claims 23 to 27, further comprising a Device for generating a magnetic field comprises Application of a magnetic field to that arranged on the base plate Powder.